The project will serve the laboratory mission in the areas of basic research and the development of sensors and medical diagnostics for bio-threat reduction. Detection of breast cancer continues to be a challenge. This is alarming when the morbidity rate of 100,000 per year from the disease is considered. Early detection of the disease would greatly decrease this fatality rate. One potential method of doing that is the detection of tumor- specific markers in the organ of interest, the breast. This requires sensitive and specific technology. We propose here to adapt the optical waveguide-based biosensor developed at Los Alamos National Laboratory to the sensitive detection of tumor markers in patient nipple aspirate fluid (NAF). This is a sandwich immunoassay approach that utilizes the physical properties of the waveguide to obtain an enhanced signal and minimize non- specific interference. If deemed feasible, this could allow for the detection and characterization of breast cancer antigens in nipple aspirate fluid thereby allowing for early detection of the disease. These markers are valuable in prognosis and determination of therapy efficacy and disease relapse as well. The use of tumor markers is limited mainly by the lack of sensitive technology. We here at Los Alamos, possess a platform that could validate the use of this approach. It is also stressed that if this is feasible, the approach can be extended to the detection of several other types of cancers.